Machines establish the groundwork of manufacturing industry, due to all products are produced by machines. Furthermore, machine tools establish the groundwork of mechanical industry due to all manufacturing processes require machine tool. Therefore, with the development in industry and the advancement in technology, the machine tool industry will be progressed as well. Because bio-medical industry, telecommunication industry and optoelectronic industry ramp recently, current related products have developed to be more miniaturized, for example, micro optical components of high-speed signal transmission, micro-sensors, micro holes of optical fibers and photolithography. Accordingly, the micro/meso-scale manufacturing technology is the key point in the oncoming fabrication technology.
In industrial applications, precise machining is based on high precision positioning technology. Therefore, how to enhance precise positioning is an important index in promotion of industry. The difficulties of the precise positioning technology resulted from too many uncertain factors. Generally, the factors, which are not concerned in large-scale positioning, should be concerned in micro/nano scale positioning.
The wet etching, plasma etching, LIGA process, electron beam, ion beams and so on are used in nano-scaled machining, thus resulting in the development of micro-electro mechanical system (MEMS). Generally speaking, MEMS technology is applied in the fabrication of about 2D to 2.5D geometry, and the relative precision of fabrication is limited to about 10-1 to 10-2 millimeter. However, for many 3-D miniaturized products having requirements of higher precision and complex shape, the MEMS technology is not able to meet the requirements. Besides, another bottleneck of the MEMS technology is that it can not be applied to metallic material or other diversified materials. Furthermore, scanning tunneling microscope (STM) or atomic force microscope need to be used in nano-scaled fabrication, but the operation speed is lower and the technique is not mature yet.
Currently, machine tools of multi-axles are serial connected mechanism. This serial connected mechanism, which is similar to cantilever beams, has a larger working area, but it may deform or have displacement due to external loading or its weight. Therefore, only the conventional servo system of serial connected mechanism of higher precision may achieve the precision of sub-micron or even nano-meter scaled. However, the requirements of the related control technique are very strict, and the cost of the whole equipment is effectively increased. Besides, machines features the piezoelectric actuators also have the problems of smaller stroke and hysteresis.
Generally, platforms of meso-scale machine tools, such as milling machines, are being directly placed on ballscrews and then driven by motors to move. Intrinsic or extrinsic vibration will affect machine tools operation and precision at the same time. Refer to FIG. 1, FIG. 1 shows a Taiwanese patent publication No. 302862, which discloses a toggle-type positioning platform, as a prior art. A screw rod 202 connects with a second platform 204 by a linkage 206, wherein the moving direction of the second platform 204 is perpendicular to the screw rod 202. When the screw rod driven by a motor 208 to rotate, the linkage 206 and the second platform 204 start to move along a predetermined path 210. To overcome the aforesaid disadvantages, the linkage 206 being disposed between the screw rod 202 and the second platform 204. Since the length L of the linkage 206 is fixed and the displacement of one end of the linkage 206 on the screw rod 202 is known, therefore the perpendicular distance H from the connecting portion to the screw rod 202 can be calculated from the trigonometric and geometric relationship. According to the numerical analysis data of the prior art, when the displacement of the screw is very small, the smaller distance H and higher positioning precision ΔH may be attained. Therefore, the length of the linkage, the displacement of the screw rod, the angle between the linkage and screw rod and other factors may affect the resolution and sensitivity of the platform. The method described above may provide higher precision of the machine tool, but the move speed of the platform is relatively low. Therefore, the present invention discloses tri-joints with one axial toggle-type machine to overcome the aforesaid disadvantages. Moreover, by the calculation of trigonometric functions, the precision of the platform can be less affected by extrinsic force and vibration and, at the same time, increase the move speed of the platform.